The long term objective of this proposal is an understanding of the processing of signals buried in a noise background, in the normal and pathologic ear. The deleterious effects of noise on the speech discrimination abilities of the hearing-impaired are well known. The utility of recent technical advances in the development of digital hearing aids and cochlear implants will depend on whether they allow users successful speech discrimination in the real world. This necessitates the development of successful noise- suppression algorithms in these devices. One positive step in the development of these algorithms is an understanding of how the normal auditory system processes signals-in-noise. This document is a proposal to study electrophysiologic correlates of signal-in- noise processing in the auditory system of humans and gerbils. The more modest specific aims of the present application include the following: 1. Extending our understanding of the effects of broadband masking noise on the human BAER; 2. Optimizing the stimulation and recording parameters for the high-pass subtractive-masking technique in humans; 3. obtaining the necessary BAER data to establish the gerbil (or, as necessary, an alternative animal species) as a viable animal model for the study of the effects of broadband and high-pass masking on the BAER; and 4. To perform several pilot experiments evaluating the effects of broadband masking noise on the neuronal responses in the eight nerve and cochlear nucleus in the gerbil.